Removable and replacement stocks for rifles are well known. Stocks often include telescoping cheek rests and telescoping butt plates, for increased comfort of the shooter. However, the length of the stock can only be adjusted by providing different locations along the buffer tube holder for locking the stock. In order to readjust the length, the rifle must be removed from the user's shoulder, the buffer tube holder unlocked, the buffer tube adjusted inside the buffer tube holder, the buffer tube holder locked again, and only then the rifle is ready for use.
In general, in order to replace the stock of an M16-type carbine or commando rifle, the buffer tube may also have to be replaced, since there is no standard diameter for buffer tubes for short M16-type firearms.
There are also known extendable cheek rests. These can be extended manually, by lifting or pressing to the desired extension above the stock, or incrementally by rotating a knob.